1. Technical Field
The present invention relates to a measurement apparatus, a measurement method, and an ultrasonic measurement apparatus.
2. Related Art
It is known that the speed of sound passing through physical matter changes according to temperature and that the amount of this change differs according to the type of physical matter. For example, it is known that the speed of sound when propagating through muscle or internal organs, which contain a large amount of water, and the speed of sound propagating through fat cells experience different changes in speed in response to changes in temperature. Therefore, it is known that by applying ultrasonic waves to the liver or the like and measuring the change in speed of a reflected ultrasonic signal in response to a change in temperature of the liver, the liver can be diagnosed as being a fatty liver or not, as shown in International Publication WO 2011/125549, for example.
However, the change in speed of the ultrasonic wave that is dependent on the physical matter in this way is indicated by only a slight difference between approximately +2 m/s·° C. in water and approximately −4 m/s·° C. in fat cells, and therefore the received ultrasonic reflected signal must be processed through an A/D conversion with a high speed sampling rate of at least several hundred MHz. Furthermore, when the measurement point fluctuates due to breathing or the like during measurement, there is an error in the measurement results, and therefore signal processing such as calculating the correlation of a plurality of pieces of data is necessary, which increases the physical dimensions of the measurement apparatus.